1. Field of the Invention
Embodiments of the invention generally relate to electrochemical plating systems, and in particular, electrochemical plating systems having an anode that is separated from a plating electrode by a multilevel diffusion differentiated permeable membrane.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio (greater than about 4:1, for example) interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill these interconnect features. However, as the interconnect sizes decrease and aspect ratios increase, void-free interconnect feature fill via conventional metallization techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as promising processes for void free filling of sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate (or a layer deposited thereon) may be efficiently filled with a conductive material, such as copper, for example. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface features of the substrate, and then the surface features of the substrate are exposed to an electrolyte solution, while an electrical bias is simultaneously applied between the substrate and a copper anode positioned within the electrolyte solution. The electrolyte solution is generally rich in ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these ions to be urged out of the electrolyte solution and to be plated onto the seed layer.
An ECP plating solution generally contains several constituents, such as, for example, a copper ion source, which may be copper sulfate, an acid, which may be sulfuric or phosphoric acid and/or derivatives thereof, a halide ion source, such as chlorine, and one or more additives configured to control various plating parameters. Additionally, the plating solution may include other copper salts, such as copper fluoborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, or copper cyanide, for example. The additives, which are often organics, may be, for example, levelers, inhibitors, suppressors, brighteners, accelerators, or other additives known in the art. These additives are typically materials that adsorb onto the surface of the substrate being plated. Useful suppressors typically include polyethers, such as polyethylene glycol, or other polymers, such as polyethylene-polypropylene oxides, which adsorb on the substrate surface, slowing down copper deposition in the adsorbed areas. Useful accelerators typically include sulfides or disulfides, such as bis(3-sulfopropyl) disulfide, which compete with suppressors for adsorption sites, and operate to facilitate copper deposition in the adsorbed areas. Useful levelers typically include thiadiazole, imidazole, and other nitrogen containing organics. Useful inhibitors typically include sodium benzoate and sodium sulfite, which operate to somewhat inhibit the rate of copper deposition on the substrate.
One challenge associated with ECP systems is that several of the components/constituents generally used in plating solutions are known to react with the surface of the copper anode. This reaction generally operates to deplete or consume the solution constituents, and therefore, renders the concentration of the particular constituents in the plating solution lower than desired. For example, is has been shown that constituent contact with the anode contributes upwards of 75% or more of the consumption or depletion of organic constituents in plating solutions. Another challenge associated with ECP systems is that contaminants produced at the surface of the anode, i.e., copper balls, are known to cause plating defects.
Therefore, there exists a need for an electrochemical plating cell configured to prevent solution additives from coming into contact with the anode. Additionally, there exists a need for an electrochemical plating cell configured to prevent contaminants generated at the anode surface from traveling to the plating electrode and causing defects in the plating process.